On the Large Achromatic at Paris. 287 



420, which could not be overlooked by the most careless observer, 

 and with 560 both stars were admirably denned. Measures of 

 position and of distance might have been gotten with the greatest 

 facility, but for want of a micrometrical apparatus. It was my in- 

 tention to have submitted the instrument, which was placed at my 

 disposal by our amiable and ever-toiling friend, Monsr. Bouvard,. 

 in the most unreserved manner possible, to other and more severe 

 tests ; but in elevating the telescope to i Bootis, the stand became 

 deranged, and the instrument was rendered unmanageable. On 

 a subsequent night, a similar accident also foiled us in our at- 

 tempts to investigate its power. 



I need not inform yow, that a telescope having an object glass 

 of the diameter above mentioned, which with these powers will 

 neatly define the limb of the planet Venus, and will give to the 

 discs of the double stars here named, images absolutely round, 

 deserves to be well spoken of. Indeed I have no hesitation in 

 saying, that this telescope is the best achromatic I ever pointed 

 to the heavens ; nor will I withhold my regret, or even the mor- 

 tification I feel in asserting, that England, when I visited it in 

 May last, could not produce an achromatic any thing like it. The 

 stand upon which it is mounted is not provided with any means 

 of giving to the telescope equatorial motion. I hope, however, 

 that the Board of Longitude of Paris, in their accustomed zeal 

 for the promotion of astronomical science, will, ere long, render 

 this noble instrument more available to the purposes of scientific 

 research, by voting to it the indispensable attributes of an equa- 

 torial. Gambeys' mechanical head would soon convert it into an 

 instrument, which would be worthy of the French nation. 



Whilst, however, I say thus much, I am far from entertaining 

 the sentiments of Mr. Fraunhofer as to the decided superiority of 

 refractors over reflectors ; nor can I accompany Mr. Struve in his 

 idea that the Dorpat telescope " may perhaps rank with the most 

 celebrated'of all reflecting telescopes, namely, Herschel's;" it is 

 true, I have not had the enviable gratification of having seen the 

 former ; still I think the Paris telescope furnishes me with data, 

 upon which to form something like a rational conjecture. Its 



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